The present invention relates generally to a system for reproducing video signals from a magnetic tape in such a manner of obtaining a slow-motion reproduction picture, or a still reproduction picture, and more particularly to a system for carrying out slow-motion reproduction and still picture reproduction without accompanying any noises or beats on a reproduced picture screen.
The prior art uses a system wherein a video signal is recorded on a magnetic tape on parallel tracks formed obliquely to the longitudinal direction of the magnetic tape. This tape travels at a tape speed which is different from that used at the time of recording or stops thereby to carry out speed-change reproduction such as quick-motion reproduction, slow-motion reproduction, or still picture reproduction. In this system, the tape speed at the time of reproduction is different from that at the time of recording, therefore the path (track) which the head traces on the tape during reproduction is different from the path (track) traced by the head during recording.
On the one hand, a conventional video signal recording and reproducing system, ordinarily, forms tracks on a recording medium in a manner which leaves an unrecorded zone or band called a guard band between neighboring tracks in order to prevent the generation of beats caused by the reproduced signals of neighboring tracks due to tracking deviation of the head at the time of reproduction. When a tape recorded in this manner is played back by speed-change reproduction as described above, the head traces over the track and the unrecorded band. When the head traces over the unrecorded band, the reproduced signal is remarkably lowered in level or disappears. For this reason, a noise is generated in the reproduced picture. Furthermore, in the above mentioned system, since unrecorded bands are provided between tracks, the utilization efficiency of the tape has been poor.
In addition, there has been a system wherein the angle of inclination of the tape relative to the head rotating plane is varied in accordance with the tape speed so that the heads will trace accurately over the track at the time of speed-change reproduction. However, this system has been accompanied by the problem of the complexity of the mechanism for varying the inclination angle of the tape in this manner, which gives rise to high cost of the apparatus, and by the difficulty of accurate tracking in actual practice.
On the other hand, the present applicant has previously described a system wherein tracks are formed on a tape without gaps between neighboring tracks, and, moreover, a color video signal can be recorded and reproduced without the occurrence of beat disturbance, in the U.S. patent application Ser. No. 731,935 entitled "Color video signal recording and/or reproducing system" filed Oct. 13, 1976, now U.S. Pat. No. 4,178,606, issued Dec. 11, 1979 and assigned to the assignee of this application. In this previously described system, a pair of azimuth heads having gaps which are inclined with a certain azimuth angle in mutually opposite directions with respect to the direction perpendicular to the longitudinal direction of the track are used, and neighboring tracks are formed in contiguous contact side-by-side without a gap therebetween. Furthermore, the phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period, and, moreover, the direction of this phase shifting is reversed from one track to the neighboring track. In accordance with this system, the tape utilization efficiency is high since the tracks are in close contact with each other, and, moreover, there is no occurrence of beat disturbance.
Then, the present applicant has proposed a new system wherein, in addition to adoption of the above described system, a plurality of rotating heads having gaps the centers thereof in the track width direction being different in height positions with respect to the rotational planes in which the heads travels are used, and the magnetic tape is caused to travel at a speed V which is represented by the equation ##EQU1## wherein Vo is the tape speed for normal reproduction (and recording), and n is a positive or negative integer, or to stop thereby to carry out slow-motion reproduction or still picture reproduction, in the U.S. patent application Ser. No. 892,147 entitled "Video Signal Speed-Change Reproducing System" filed on Mar. 31, 1978, and assigned to the assignee of this application, and subsequently abandoned. A continuation-in-part application Ser. No. 58,818 was filed on July 19, 1979.
This latter proposed system is capable of carrying out slow-motion reproduction or still picture reproduction with least noise. However, the magnetic tape is required to travel at the speed satisfying the above given equation, which gives rise to a problem in that slow motion reproduction at any given speeds can not be carried out. Moreover, when the traveling magnetic tape is to be stopped for still picture production, the position where the magnetic tape stops is not controlled. Accordingly, the operator is required to search the position where the magnetic tape stops with least or no noise while observing the reproduced picture screen. Thus, there arises a problem in that operation becomes rather troublesome.